Probably a bit late, but I'm a convert to SPD-SL over Keos. Cleats and pedals way more durable, and the tension can be ratcheted up higher than Keos. No real difference between 105 and Ultegra pedals bar the finish and a little bit of weight, not tried the Dura-Ace ones. Top tip - go to Evans and get them to price match Ribble on the 105s for about 35 quids
Not too late!
Many thanks, great info.